Lingering thunderstorms delayed the start at Royal Liverpool by 30 minutes, and three millimetres of overnight rain softened the fiery fairways, making scoring easier than it had been on the sizzlingly hot practice days.

Mansfield's Owen, who picked up four shots inside the last six holes, set the early clubhouse lead in sunny mid-morning conditions.

He was briefly overtaken by Londoner Wall, who eagled the 10th and 16th before slipping back at the next hole.

I played well enough to score three under, but I couldn't get the ball in the hole

Scotland's Colin Montgomerie

But McDowell, 26, who was 11th at St Andrews last year, maintained his advantage with a bogey-free afternoon round.

The former top US college golfer went out in 32 with birdies at the 5th, 7th and 9th, the latter after holing out from the greenside bunker.

He picked up further shots at 10 and 11 before a final birdie on the short 16th.

"It's no good leading the Open on Thursday, I have to lead it on Sunday," he said, adding that his links background in Portrush gave him "an extra 5% on most of the field".

World number one Woods, 30, got off to a bad start with a bogey on the 1st but clawed shots back at the 5th and short 9th.

And the 10-time major winner, not yet at his scintillating best, battled his way to three under after 16 before eagling the long 18th from 15 feet.

"The key is to just keep playing yourself back," said Woods. "If you hit good shots you can make birdies."

The group on four under also included former US Open winner Jim Furyk, Finn Mikko Ilonen, the 2000 British amateur champion at Hoylake, US Ryder Cup captain Tom Lehman and Canada's former Masters champion Mike Weir.

Howell, who carded 74, has a poor record in the Open

America's world number two Phil Mickelson, England's Lee Westwood, Lee Slattery and Robert Rock and Northern Ireland's Darren Clarke all handed in 69s for three under.

Another stroke adrift were Wales' Bradley Dredge, Fiji's world number three Vijay Singh, America's former winner David Duval and two-time US Open champion Retief Goosen of South Africa.

Scotland's Montgomerie, who blew a golden chance to win his maiden major at the US Open in June, birdied the first but endured an off day with the putter as he leaked four bogeys to two further birdies.

"I played well enough to score three under," said Montgomerie. "But I couldn't get the ball in the hole."

At seven shots back, Montgomerie, last year's runner-up, is not completely out if it but several of Europe's big hopes fared even worse.

English duo Luke Donald and Order of Merit leader David Howell carded two-over 74s, one better than Ireland's Padraig Harrington and another Englishman Ian Poulter, who triple-bogeyed the 14th.

Spanish great Seve Ballesteros, playing with Poulter, also compiled a 74 in his first Open since 2001.

The 49-year-old three-time Open champion, who had 15-year-old son Baldomero as his caddie, has hardly played in recent years because of injuries and a serious slump in form.

"It was nice to walk the fairways of an Open Championship, especially with my son - that was fantastic," said the popular Ballesteros. "I tried as hard as I could. I played with the heart as always."

England's former world number one Nick Faldo, himself a three-time Open winner and with teenage son Matthew on his bag, carded a five-over 77 alongside Woods.

There was scant communication between the two, though they appeared to have buried the hatchet after a midweek spat.

Friday's second round is due to get under way at 0630 BST, with a forecast of sunny intervals and cooler temperatures of 22C, getting hotter again at the weekend.